This invention relates to a method of brazing aluminum or aluminum alloy materials.
More particularly, in a method of brazing aluminum products in which fluoride fluxes which are not hygroscopic after brazing and are not corrosive against aluminum are employed for removing oxidized films from surfaces of the aluminum or aluminum alloy products and hard solders for brazing them, this invention is to provide a step in which the fluoride fluxes are produced continuously and in situ with stable compositions and with high productivity, and which enables the brazing method to be completely continuous.
As a flux for brazing aluminum materials which is not corrosive against aluminum, fluoride fluxes have been used. They are fluorides of a melting point of about 565.degree. C. to about 575.degree. C. containing a simple substance of KAlF.sub.4 or K.sub.3 AlF.sub.6. They are generally produced by (a) mixing KF and AlF.sub.3 powders to obtain a paste which is in turn dried, or (b) heating powders of KF and AlF.sub.3 to a molten mixture which is pulverized after having been cooled and solidified.
The above conventional method (a) can be represented by a method described in U.K. Pat. No. 1,055,914, in which AlF.sub.3 of 53-55% and KF of 47-45% both of which are powder forms are made to a paste by adding thereto water and stiring them, and they are dried at a temperature below 200.degree. C. It is held that in this method (a), AlF.sub.3 and KF can hardly complete their reactions since AlF.sub.3 is hardly soluble to water. Reaction products of this method (a) are accordingly not stable at their compositions. They have drawbacks that when they are made to an aqueous suspension, KF which has not reacted forms a solution whereby a brazing temperature easily varies.
The above-mentioned conventional method (b) is described for example in Japanese patent publication No. 58-27037, in which in order not to have KF remained unreacted, powders of AlF.sub.3 and KF are mixed, heated, and melted. The molten mixture is pulverized after solidified.
These methods (a) and (b) can hardly be incorporated into a brazing method as a step thereof which can produce a flux in situ in the continuous brazing method, because the method (a) can hardly give a flux of a stable and constant composition whereby a brazing temperature has to be changed frequently, and the method (b) relies upon a batch production which does not match with a continous brazing operation.